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Arnestad, Håvard; Rindal, Ole Marius Hoel; Austeng, Andreas & Näsholm, Sven Peter
(2024).
Estimation of probability densities in ultrasound imaging.
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Han, Chaoran; Arnestad, Håvard; Austeng, Andreas & Näsholm, Sven Peter
(2024).
Spectral estimation inspired by a non-linear beamformer: Insights into null-subtraction imaging.
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Näsholm, Sven Peter; Arnestad, Håvard; Austeng, Andreas & Rindal, Ole Marius Hoel
(2023).
Calculating the generalized contrast-to-noise ratio using kernel density estimation.
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The histogram-based generalized contrast-to-noise ratio (gCNR) evaluates how well image regions with different intensity can be distinguished. The gCNR is defined as ‘one minus the overlap region’ of normalized histograms from two regions. Histogram-based gCNR depends on user parameters like bin size and bin offset, but there are also approaches to robustify the histogram calculation.
Kernel density estimation (KDE) is a well-established alternative to histograms to estimate probability density functions (PDFs), and is generally considered to be more robust. We suggest replacing histograms with KDE in gCNR calculations.
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Gereb, Gabor & Arnestad, Håvard
(2023).
Interval computations in acoustics.
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Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter
(2023).
Bounding the beampattern of acoustic arrays using interval arithmetic.
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Viggen, Erlend Magnus & Arnestad, Håvard
(2023).
Why leaky flexural plate waves misbehave at low frequencies.
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Austeng, Andreas; Arnestad, Håvard; Bjåstad, Tore Grüner; Måsøy, Svein-Erik & Rindal, Ole Marius Hoel
(2022).
Issues with Histogram Matching for Fair Evaluation of Image Quality Metrics.
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Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter
(2022).
Bounding the beampattern of acoustic arrays using interval arithmetic.
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Arnestad, Håvard & Viggen, Erlend Magnus
(2022).
A Fast Simulation Method for Lamb Wave Propagation in Coupled Non-Parallel Plates.
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Arnestad, Håvard; Austeng, Andreas; Näsholm, Sven Peter & Rindal, Ole Marius Hoel
(2022).
The Effect of Retrospective Transmit Focusing on Minimum Variance Beamforming.
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Viggen, Erlend Magnus & Arnestad, Håvard
(2022).
An explanatory model for sound radiation from subsonic surface vibrations.
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Surface vibrations will generate pressure waves in an adjacent fluid. It is commonly held that these waves radiate away from the surface only if the vibration is supersonic, i.e., faster than the fluid's sound speed. However, multiple articles have shown mathematically that even subsonic vibrations can yield radiating waves. Even so, the physical understanding of this phenomenon has been insufficient. In our work, we derive and validate an explanatory physical model to provide such an understanding.
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Arnestad, Håvard; Gereb, Gabor; Birkenes Lønmo, Tor Inge; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter
(2022).
Sonar array beampattern bounds: tolerance analysis using interval arithmetic.
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The framework of interval arithmetic (IA) and its extension to complex numbers has in the last decade been applied as a tool for finding robust tolerance bounds of antenna arrays. The IA framework complements statistical methods, as inclusive upper and lower bounds of the beampattern are obtained directly, only assuming error bounds on specifically chosen array parameters.
Recently, beampattern synthesis for sonar arrays subject to amplitude excitation errors has been extended from linear arrays with omnidirectional elements to non-linear arrays with directive elements. In this work, we demonstrate that the analysis can be developed further to include both amplitude and phase errors. Moreover, we account for error bounds in element position and orientation, thus representing a more comprehensive method for evaluating the worst-case performance due to uncertainty bounds in a multitude of design parameters.
For this purpose, we have created an open-source MATLAB toolbox to calculate beampattern bounds for an array with bounded error tolerances. The toolbox features an object oriented library of interval classes and an interactive graphical user interface with easily configurable settings, where results for different interval representations are shown along with their corresponding bounds. The beampattern bounds of a sonar array is illustrated through an example.
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Arnestad, Håvard & Viggen, Erlend Magnus
(2022).
A fast method for simulating Lamb wave propagation in coupled non-parallel plates.
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Viggen, Erlend Magnus & Arnestad, Håvard
(2022).
Intensity of inhomogeneous waves in simple solids.
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Arnestad, Håvard Kjellmo & Viggen, Erlend Magnus
(2021).
A fast semi-analytical method for propagating leaky Lamb wavefields.
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A fast method is presented for calculating the wavefields from initialized leaky Lamb waves on plates immersed in sufficiently light fluids. The method works by precomputing the dispersion relation and attenuation, and propagating the wavefields in the frequency domain. An angular spectrum approach is used to include leakage into surrounding fluid. Compared to matching FEM simulations, the computations are performed in the order of seconds, rather than hours. The method also benefits from being much easier to set up correctly, but is on the other hand less general in that it cannot handle e.g. scattering from defects. The correspondence is shown to be good for the case of interest.
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Viggen, Erlend Magnus & Arnestad, Håvard Kjellmo
(2021).
Understanding sound radiation from surface vibrations moving at subsonic speeds.